U.S. patent application number 11/321254 was filed with the patent office on 2007-07-05 for metallic foam trap for poisons: aircraft ozone.
Invention is credited to Michael Patrick Galligan, Rudolph H. Lechelt.
Application Number | 20070154375 11/321254 |
Document ID | / |
Family ID | 38224628 |
Filed Date | 2007-07-05 |
United States Patent
Application |
20070154375 |
Kind Code |
A1 |
Galligan; Michael Patrick ;
et al. |
July 5, 2007 |
Metallic foam trap for poisons: aircraft ozone
Abstract
The present invention is directed to an improved apparatus and
method of minimizing catalyst poisoning by inorganic deposits from
lube oil additives and particulate matter, especially in aircraft.
More specifically, the present invention is directed to an air
purification system comprising an upstream metallic foam trap and
downstream converter, wherein the trap physically blocks inorganic
deposits and particulate matter from poisoning the downstream
catalysts. The present invention is also directed to a metallic
foam trap containing a coat comprising a first metallic thermal arc
sprayed layer and optionally a second refractory metal oxide.
Inventors: |
Galligan; Michael Patrick;
(Cranford, NJ) ; Lechelt; Rudolph H.; (Edison,
NJ) |
Correspondence
Address: |
Chief Patent Counsel;Engelhard Corporation
101 Wood Avenue
P.O. Box 770
Iselin
NJ
08830-0770
US
|
Family ID: |
38224628 |
Appl. No.: |
11/321254 |
Filed: |
December 29, 2005 |
Current U.S.
Class: |
423/219 ;
422/177 |
Current CPC
Class: |
B01D 2257/708 20130101;
B64D 2013/0685 20130101; B01D 53/8675 20130101; B01D 53/885
20130101; B60H 3/0085 20130101; B01D 2257/106 20130101; B01D
2257/90 20130101 |
Class at
Publication: |
423/219 ;
422/177 |
International
Class: |
B01D 53/66 20060101
B01D053/66 |
Claims
1. In an air recirculation system for redirecting purified air into
an aircraft cabin comprising an inlet, an air purification system,
and an air outlet for redirecting said purified air into said
aircraft cabin, said air purification system further comprising:
(a) an upstream metallic foam trap; and (b) a downstream converter,
said converter comprising one or more catalysts for abatement of
ozone and/or volatile organic compounds.
2. The apparatus of claim 1, wherein said metallic foam is selected
from the group consisting of stainless steel, copper, titanium,
Fecralloy, aluminum zirconate, aluminum titanate, aluminum
phosphate, cordierite, mullite and corundum.
3. The apparatus of claim 1, wherein said metallic foam trap is an
aluminum, copper, titanium, or titanium aluminum alloy comprising
trap.
4. The apparatus of claim 1, wherein said metallic foam trap is
coated with a metallic thermal arc sprayed layer.
5. The apparatus of claim 2, wherein said metallic thermal arc
sprayed layer is selected from the group consisting of Ni, Ni/Al,
Ni/Cr, Ni/Cr/Al/Y, Co/Cr, Co/Cr/Al/Y, Co/Ni/Cr/Al/Y, Fe/Al, Fe/Cr,
Fe/Cr/Al, Fe/Cr/Al/Y, Fe/Ni/Al, Fe/Ni/Cr, 300 and 400 series
stainless steels.
6. The apparatus of claim 2, wherein said metallic foam is coated
with said metallic thermal arc sprayed layer and a refractory oxide
layer.
7. The apparatus of claim 4, wherein said refractory oxide layer is
selected from the group consisting of refractory oxides such as
copper, alumina, gamma-alumina, titania, zirconia,
zirconia-alumina, zirconia-titania, titania-alumina,
lanthana-alumina, baria-zirconia-alumina, niobia-alumina, and
silica-leached cordierite.
8. The apparatus of claim 1, wherein said converter comprising one
or more catalysts is a dual-function converter for the abatement of
volatile organic compounds and ozone.
9. A method for the abatement of ozone and volatile organic
compounds from aircraft cabin air, said method comprising: (a)
receiving an inlet air stream from an aircraft, (b) directing said
inlet air stream through: (i) an upstream metallic foam trap; and
(ii) a downstream converter for abatement of ozone and/or volatile
organic compounds; and (c) recirculating said air stream from said
downstream converter to said aircraft cabin.
10. The method of claim 9, wherein said metallic foam is selected
from the group consisting of stainless steel, copper, titanium,
Fecralloy, aluminum zirconate, aluminum titanate, aluminum
phosphate, cordierite, mullite and corundum.
11. The method of claim 9, wherein said metallic foam trap in an
aluminum, copper, titanium, or titanium aluminum alloy comprising
trap.
12. The method of claim 9, wherein said metallic foam trap is
coated with a metallic thermal arc sprayed layer.
13. The method of claim 12, wherein said metallic thermal arc
sprayed layer is selected from the group consisting of Ni, Ni/Al,
Ni/Cr, Ni/Cr/Al/Y, Co/Cr, Co/Cr/Al/Y, Co/Ni/Cr/Al/Y, Fe/Al, Fe/Cr,
Fe/Cr/Al, Fe/Cr/Al/Y, Fe/Ni/Al, Fe/Ni/Cr, 300 and 400 series
stainless steels.
14. The method of claim 12, wherein said metallic foam is coated
with said metallic thermal arc sprayed layer and a refractory oxide
layer.
15. The method of claim 14, wherein said refractory oxide layer is
selected from the group consisting of refractory oxides such as
copper, alumina, gamma-alumina, titania, zirconia,
zirconia-alumina, zirconia-titania, titania-alumina,
lanthana-alumina, baria-zirconia-alumina, niobia-alumina, and
silica-leached cordierite.
16. The apparatus of claim 9, wherein said conversion catalyst is a
dual-function catalyst for the abatement of volatile organic
compounds and ozone.
17. In an air recirculation system for redirecting purified air
into an aircraft cabin comprising an inlet, an air purification
system, and an air outlet for redirecting said purified air into
said aircraft cabin, said air purification system further
comprising: (a) an upstream metallic foam trap said foam trap
containing at least one perforated skewed channel therethrough; and
(b) a downstream converter, said converter comprising one or more
catalysts for abatement of ozone and/or volatile organic
compounds.
18. The apparatus of claim 17, wherein said metallic foam is
selected from the group consisting of stainless steel, copper,
titanium, Fecralloy, aluminum zirconate, aluminum titanate,
aluminum phosphate, cordierite, mullite and corundum.
19. The apparatus of claim 17, wherein said metallic foam trap is
coated with a metallic thermal arc sprayed layer.
20. The apparatus of claim 19, wherein said metallic thermal arc
sprayed layer is selected from the group consisting of Ni, Ni/Al,
Ni/Cr, Ni/Cr/Al/Y, Co/Cr, Co/Cr/Al/Y, Co/Ni/Cr/Al/Y, Fe/Al, Fe/Cr,
Fe/Cr/Al, Fe/Cr/Al/Y, Fe/Ni/Al, Fe/Ni/Cr, 300 and 400 series
stainless steels.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to an apparatus and
method for the improvement of air quality. More specifically, the
present invention relates to an apparatus and method for improved
abatement of ozone and volatile organic compounds (VOCs) from air,
particularly from aircraft cabin air.
BACKGROUND OF THE INVENTION
[0002] A commercial aircraft usually includes an environmental
control system for providing a stream of cooled, conditioned air to
an aircraft cabin. A typical environmental control system receives
compressed air such as bleed air from a compressor stage of an
aircraft gas turbine engine, expands the compressed air in a
cooling turbine and removes moisture from the compressed air via a
water extractor.
[0003] Toxic ozone in the compressed air becomes an issue when an
aircraft is cruising at altitudes that exceed 20,000 feet. To
reduce the ozone to a level within satisfactory limits, the
environmental system is provided with an ozone-destroying catalytic
converter.
[0004] There are a number of desirable characteristics for an
ozone-destroying catalytic converter of an aircraft. These
characteristics include a) high efficiency of ozone conversion at
bleed air operating temperature; b) good poison resistance from
humidity, sulfur compounds, oil, dust, and the like, which may be
present in the compressed air (for long life and minimum system
overhaul and maintenance costs); c) light weight to minimize system
parasitic load; d) high structural integrity of catalyst support
under extreme heat and/or vibration shock, which may arise during
normal flight conditions (also for long life and minimum system
overhaul and maintenance costs); and e) high mass transport
efficiency with low pressure drop.
[0005] Among the various ways known to eliminate ozone
contamination from an air stream by decomposition of the ozone into
oxygen are catalytic substances including metallic and non-metallic
catalysts. Although catalytic systems appear to be the most
efficient way to remove ozone from the bleed air or pneumatic
ducting air supply system of an aircraft, many of such catalytic
substances e.g. in the form of pellets or particles, must be
carried in a container or canister, which creates problems with
regard to weight as well as affecting the air flow. These materials
also have other disadvantages. Thus, for example, the use of a
catalyst coating on a metal substrate is sacrificial, in that the
resultant catalyst coated oxide is readily removed and lost in the
air stream. Although nickel is satisfactory it requires a very
clean surface for deposition of the metal.
[0006] Many systems are known in the art for the removal of ozone
from air, including those disclosed in the following U.S. patents.
U.S. Pat. No. 5,422,331, incorporated herein by reference,
discloses methods and catalyst compositions for abating noxious
substances, particularly ozone, contained in air. The treatment of
carbon monoxide, hydrogen sulfide and hydrocarbons is also
discussed. A primary focus of this patent is methods of treating
air taken into and/or circulated in aircraft cabins, with the
cabins of trains, buses and other vehicles being mentioned as well.
The patent also indicates that the disclosed catalysts can be used
to abate ozone in equipment, such as xerographic copy machines,
which generate ozone. Further, the patent indicates that the
catalysts can be applied to surfaces in air handling systems for
residences, office and factory buildings, public buildings,
hospitals and the like. For this method, the catalyst can be
applied to existing substrates of the air handling system, such as
fan blades in air handling fans or compressors, grills, louvers or
any other surface exposed to the air stream.
[0007] U.S. Pat. No. 4,206,083, incorporated herein by reference,
discloses the co-precipitation of platinum, palladium and manganese
oxide on a ceramic support, such as a cordierite support, in order
to provide a catalyst suitable for the reduction of ozone content
of air intended for human respiration. The patent refers to U.S.
Pat. No. 3,269,801 as evidence that it had been long recognized
that ozone is present in the atmosphere in toxic concentrations at
high altitudes. Aircraft flying at those altitudes scoop in cabin
air from the outside atmosphere which, because it is very much
compressed, is raised in temperature to several hundred degrees
centigrade. Such air is treated to reduce the ozone concentration
of it to below 1 part per million ("ppm") to render it fit for use
as cabin air.
[0008] U.S. Pat. No. 5,187,137, incorporated herein by reference,
discloses an ozone abatement catalyst comprising a composition
containing manganese oxide and metallic palladium and/or palladium
oxide as the essential ingredients, formed as a thin film on a
support. The method of preparing the catalyst includes coating on a
support a slurry containing manganese oxide, metallic palladium
and/or a palladium compound, and an inorganic oxide sol as a
binder, for example, an alumina sol, silica sol, titania sol or
zirconia sol. The patent discloses that the support, i.e., the
substrate on which the catalytic material is disposed, may be a
cordierite or other similar inorganic support, or it may be a metal
support.
[0009] U.S. Pat. No. 4,900,712, incorporated herein by reference,
discloses a catalytic washcoat in which one or more catalytically
active non-noble metal oxides ("dopants") such as iron oxide are
deposited from neutral aqueous colloidal solutions thereof onto
preformed high surface area crystalline alumina. The neutral
colloidal compounds are said to provide a uniform, thin coating of
the non-noble dopants on the alumina particles and to avoid the use
of noxious elements such as nitrates or chlorides, thereby
substantially eliminating any air pollution hazard. The reference
to eliminating air pollution hazards appears to be with reference
to the manufacture of the catalyst.
[0010] U.S. Pat. No. 4,343,776, incorporated herein by reference,
discloses an ozone abatement catalyst containing at least one
platinum group metal (platinum, palladium or rhodium) or
catalytically active compound thereof and an oxide or aluminate of
at least one non-precious Group VIII metal (iron, cobalt or
nickel). By applying the non-precious metal oxide as an alumina
slip prior to application of the platinum group metal component to
the substrate, the platinum group metal, e.g., palladium, is
preferentially exposed to the ozone. The carrier or support, i.e.,
the substrate, may be any one of a wide range of materials,
including aluminum.
[0011] U.S. Pat. No. 5,250,489, incorporated herein by reference,
discloses a catalyst structure configured to provide heat exchange
in which the support, i.e., substrate, is a metallic support which
may comprise aluminum or aluminum alloys, provided the latter are
used at temperatures which will not deform or melt the material.
However, other materials, including aluminum-containing steels are
described.
[0012] U.S. Pat. No. 5,080,882, incorporated herein by reference,
discloses an ozone decomposition catalyst disposed on a thin porous
carrier (substrate) material which has micropores of preferably not
less than 30 microns in diameter for ozone abatement, in order to
prevent substantial pressure loss. Any suitable known ozone
catalyst may be utilized, including oxides of manganese, iron,
silver, nickel or copper and a noble metal such as platinum or
palladium or a mixture of two or more of these.
[0013] In addition to the problems caused by elevated levels of
ozone in aircraft air, high levels of volatile organic compounds
(VOCs) can also cause substantial passenger discomfort. The
treatment of aircraft intake gases containing VOCs has been of
increasing concern in recent years. Catalytic oxidation and
adsorption are commonly used for removing these pollutants. In some
instances, adsorption by adsorbents such as carbon can be used;
however, this process does not destroy the pollutants, but merely
concentrates them. Furthermore, adsorption efficiency can be
adversely impacted by fluctuating concentrations of the gaseous
components. Catalytic oxidation is a more energy efficient and
economical way of destroying VOCs in air intake systems. Catalytic
oxidation operates at significantly lower temperatures and requires
smaller reactors made of less expensive materials.
[0014] Methods for the catalytic oxidation of VOCs are well known
in the art. For example, U.S. Pat. Nos. 3,972,979 and 4,053,557,
incorporated herein by reference, describe the decomposition of
halogenated hydrocarbons by oxidation over chromium oxide or a
boehmite supported platinum.
[0015] U.S. Pat. Nos. 4,059,675, 4,059,676 and 4,059,683,
incorporated herein by reference, describe methods for decomposing
halogenated organic compounds using catalysts containing ruthenium,
ruthenium-platinum and platinum, respectively, in the presence of
an oxidizing agent at a temperature of at least 350.degree. C.
[0016] U.S. Pat. No. 5,283,041, incorporated herein by reference,
discloses an oxidation catalyst for treating a gas stream
containing compounds selected from the group consisting of
halogenated organic compounds, other organic compounds and mixtures
thereof; the catalyst comprising a core material comprising
zirconium oxide and one or more oxides of manganese, cerium or
cobalt with vanadium oxide and, preferably, platinum group metal
dispersed on the core material.
[0017] U.S. Pat. No. 5,643,545, incorporated herein by reference,
relates to treatment of streams containing halogenated organic
compounds and volatile organic compounds (VOCs) with catalytic
materials deposited on high acidity and/or low acidity
supports.
[0018] U.S. Pat. Nos. 5,578,283 and 5,653,949, incorporated herein
by reference, relate to treatment of gases containing halogenated
organic compounds, non-halogenated organic compounds, carbon
monoxide or mixtures thereof. Catalyst compositions useful in the
treatment comprise at least one platinum group metal, zirconium
oxide and at least one oxide of manganese, cerium or cobalt. A
further composition disclosed uses the foregoing described
components but which is substantially free of vanadium in a process
for treating a gas stream containing at least one brominated
organic compound.
[0019] U.S. Pat. No. 6,319,484, incorporated herein by reference,
discloses a composition for abatement of airborne pollution by
volatile organic compounds ("VOCs"), having an upstream composition
containing a protective adsorbent, e.g., Y zeolite, which is
effective for adsorbing large VOC molecules. The downstream
composition contains a second adsorbent, e.g., a silver-containing
ZSM-5, which is effective for adsorbing relatively smaller VOC
molecules, e.g., propylene, and a second oxidation catalyst
intimately intermingled therewith. Oxidation of VOCs while they are
still retained on the adsorbents is promoted at temperatures lower
than would be required if the VOCs were desorbed into the gaseous
phase.
[0020] However, all of the ozone and VOC converters have
limitations. Specifically, they have relatively short useful life
spans. Currently, aircraft original equipment manufacturers look to
regenerate or replace converters every 4,000 to 15,000 flight miles
in some applications. Extending the life of these converters could
result in significant savings. The short life spans of currently
used catalysts result from pre-mature poisoning of the catalysts by
inorganic species of zinc, phosphorus, calcium, and other elements,
which may leak into the air stream from the lube oil additives used
in the engine and/or compressor.
[0021] Therefore, it is an object of the present invention to
provide an apparatus for improved purification of air, particularly
aircraft cabin air. It is another objective of the present
invention to provide a means of removing inorganic compounds and
particulate matter from inlet gas streams, thereby preventing
catalytic poisoning, and thereby extending the life of the
catalysts.
SUMMARY OF THE INVENTION
[0022] The present invention is directed to an apparatus for the
abatement of volatile organic compounds (VOCs) and ozone from
aircraft cabin air. More specifically, the apparatus comprises an
upstream metallic foam trap and a downstream converter for abating
VOCs and/or ozone. The upstream metallic foam trap of the present
invention preferentially collects poisonous species, e.g. inorganic
deposits from engine or compressor lube oils, primarily in gaseous
phase and serves as a physical barrier to the downstream
catalysts.
[0023] The present invention is also directed to a method for the
abatement of ozone and VOCs. The method comprising providing an
apparatus comprising an air purification system containing an
upstream metallic foam trap and a downstream converter for the
abatement of VOCs and/or ozone, and directing an inlet air stream
through said apparatus.
[0024] A further aspect of the present invention relates to a
metallic foam trap having a metallic layer deposited thereon by
thermal arc spraying, thereby improving trapping efficiency.
Optionally a refractory oxide material is coated on the metallic
thermal arc sprayed layer to again improve trapping efficiency. The
thermal arc sprayed layer in such application is an intermetallic
layer or anchor layer and holds the refractory oxide layer in
place.
[0025] Other objectives and advantages of the present invention
will become apparent from the following description and appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a schematic of an apparatus for the abatement of
ozone and/or volatile organic compounds in accordance with one
embodiment of the present invention;
[0027] FIG. 2a is a pictorial sectional view illustrating the
general configuration of a metallic foam trap in accordance with
one embodiment of the present invention;
[0028] FIG. 2b is an enlarged schematic fragmental view of the
three-dimensional network of the metallic foam trap;
[0029] FIG. 3 is a pictorial sectional view of an alternative
configuration of a metallic foam trap, in accordance with an
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0030] The present invention is directed to an apparatus for
improving cabin air quality, particularly in an aircraft, by
reducing the presence of volatile organic compounds (VOCS) and/or
ozone. More specifically, the present invention is directed to an
apparatus comprising of an air purification system containing an
upstream metallic foam trap, which preferentially collects
poisonous species, such as those found in lube oil additives,
primarily in gaseous phase and serves as a physical barrier to the
catalysts of a separate downstream converter for the abatement of
VOCs and/or ozone. In an embodiment of the present invention, the
metallic foam trap and the converter can be fused together by
welding, diffusion bonding or other means to constitute a single
air purification unit. In another embodiment the converter is a
dual-function converter for the abatement of both VOCs and/or
ozone.
[0031] The apparatus of the present invention may be more readily
appreciated by reference to FIG. 1, which depicts in general terms
a schematic drawing of one non-limiting embodiment of the
invention. Referring to FIG. 1, the apparatus comprises an air
inlet 2, an air purification system 4, and an air outlet 6, which
can be employed in an aircraft for the abatement of ozone and/or
volatile organic compounds (VOCs), from recirculated aircraft cabin
air and/or from compressed air received from a compressor contained
within the aircraft. The apparatus receives ambient air and/or
compressed air from a compressor contained within the aircraft,
which needs to be purified by abatement of ozone and VOCs, through
the air inlet 2 and expels the purified air through the air outlet
6 into the cabin of an aircraft 8. In turn, aircraft cabin air can
be recirculated back to the apparatus through air passage tube 14.
The air purification system comprises an upstream metallic foam
trap 10 and a downstream converter 12 containing one or more
catalysts useful for the break down of ozone and VOCs. As discussed
in further detail below, the upstream metallic foam trap 10,
comprises an open network of metallic cells or pores consisting of
struts for the cellular walls, which preferentially collects
poisonous species primarily in gaseous phase and serves as a
physical barrier to the downstream converter, see FIG. 2a and
2b.
[0032] The present invention is also directed to a method of
improving aircraft cabin air quality, wherein the method provides
an apparatus comprising an air purification system containing an
upstream metallic foam trap, which preferentially collects
poisonous species, such as those found in lube oil additives,
primarily in gaseous phase and serves as a physical barrier to the
catalysts of a separate downstream converter for the abatement of
VOCs and/or ozone, and directing an inlet air stream through said
apparatus. In an embodiment of the present invention, the metallic
foam trap and the converter can be fused together by welding,
diffusion bonding or other means to constitute a single air
purification unit. In another embodiment the converter is a
dual-function converter for the abatement of both VOCs and
ozone.
[0033] As used herein and in the appended claims, the terms
"upstream" and "downstream" refer to relative directions according
to the flow of an aircraft air inlet stream, which typically
contains high levels of ozone and may contain volatile organic
compounds (VOCs). The term "stream," as used in this specification
and appended claims, broadly refers to any combination of flowing
gas that may contain solid or liquid particulate matter.
[0034] The downstream converter of the instant invention may be
used in any configuration, shape or size, which exposes it to the
gas to be treated. For example, the catalyst can be conveniently
employed in particulate form or the catalyst can be deposited onto
a solid monolithic carrier. When the particulate form is desired,
the catalyst can be formed into shapes such as tablets, pellets,
granules, rings, spheres, etc. The particulate form is especially
desirable where large volumes of catalysts are needed, and for use
in circumstances in which frequent replacement of the catalyst may
be desired. In circumstances in which less mass is desirable or in
which movement or agitation of particles of catalyst may result in
attrition, dusting and resulting loss of dispersed metals or oxides
or undue increase in pressure drop across the particles due to high
gas flows, a monolithic form is preferred.
[0035] In the employment of a monolithic form, it is usually most
convenient to employ the catalyst as a thin film or coating
deposited on an inert carrier material which provides the
structural support for the catalyst. The inert carrier material can
be any refractory material such as ceramic or metallic materials.
It is desirable that the carrier material be unreactive with the
catalytic components and not be degraded by the gas to which it is
exposed. Examples of suitable ceramic materials include
sillimanite, petalite, cordierite, mullite, zircon, zircon mullite,
spodumene, alumina-titanate, etc. Additionally, metallic materials,
which are within the scope of this invention include metals and
alloys as disclosed in U.S. Pat. No. 3,920,583, incorporated herein
by reference, which are oxidation resistant and are otherwise
capable of withstanding high temperatures. For the treatment of
gases containing halocarbons, ceramic materials may be
preferred.
[0036] The monolithic carrier material can best be utilized in any
rigid unitary configuration, which provides a plurality of pores or
channels extending in the direction of gas flow. In one embodiment
the configuration can be a honeycomb configuration. The honeycomb
structure can be used advantageously in either unitary form, or as
an arrangement of multiple modules. The honeycomb structure is
usually oriented such that gas flow is generally in the same
direction as the cells or channels of the honeycomb structure. For
a more detailed discussion of monolithic structures, refer to U.S.
Pat. No. 3,785,998 and U.S. Pat. No. 3,767,453, which are
incorporated herein by reference.
[0037] If particulate form is desired, the catalyst can be formed
into granules, spheres or extrudates by means well known in the
industry. For example, the catalyst powder can be combined with a
binder such as a clay and rolled in a disk pelletizing apparatus to
give catalyst spheres. The amount of binder can vary considerably
but for convenience is present from about 10 to about 30 weight
%.
[0038] If a monolithic form is desired, the catalyst of this
invention can be deposited onto the monolithic honeycomb carrier by
conventional means. For example, a slurry can be prepared by means
known in the art such as combining the appropriate amounts of the
catalyst of this invention in powder form, with water. The
resultant slurry is ball-milled for about 8 to 18 hours to form a
usable slurry. Other types of mills such as impact mills can be
used to reduce the milling time to about 1-4 hours. This slurry can
now be used to deposit a thin film or coating of catalyst of this
invention onto the monolithic carrier by means well known in the
art. Optionally, an adhesion aid such as alumina, silica, zirconium
silicate, aluminum silicates or zirconium acetate can be added in
the form of an aqueous slurry or solution. A common method involves
dipping the monolithic carrier into said slurry, blowing out the
excess slurry, drying and calcining in air at a temperature of
about 450.degree. C. to about 600.degree. C. for about 1 to about 4
hours. This procedure can be repeated until the desired amount of
catalyst of this invention is deposited on said monolithic
honeycomb carrier. It is desirable that the catalyst of this
invention be present on the monolithic carrier in an amount in the
range of about 1-4 g of catalyst per in.sup.3 of carrier volume and
preferably from about 1.5-3 g/in.sup.3.
[0039] The downstream ozone abatement catalysts useful for the
practice of the present invention can be any ozone abatement
catalyst system known in the art. For example, the ozone abatement
catalysts of U.S. Pat. Nos. 4,343,776; 4,206,083; 4,900,712;
5,080,882; 5,187,137; 5,250,489; 5,422,331; 5,620,672; 6,214,303;
6,340,066; and 6,616,903, which are hereby incorporated by
reference, are useful for the practice of the present
invention.
[0040] An illustrative example is U.S. Pat. No. 6,616,903, which
discloses a useful ozone treating catalyst comprises at least one
precious metal component, preferably a palladium component
dispersed on a suitable support such as a refractory oxide support.
The composition comprises from 0.1 to 20.0 weight %, and preferably
0.5 to 15 weight % of precious metal on the support, such as a
refractory oxide support, based on the weight of the precious metal
(metal and not oxide) and the support. Palladium is preferably used
in amounts of from 2 to 15, more preferably 5 to 15 and yet more
preferably 8 to 12 weight %. Platinum is preferably used at 0.1 to
10, more preferably 0.1 to 5.0, and yet more preferably 2 to 5
weight %. Palladium is most preferred to catalyze the reaction of
ozone to form oxygen. The support materials can be selected from
the group recited above. In one embodiment, there can additionally
be a bulk manganese component, or a manganese component dispersed
on the same or different refractory oxide support as the precious
metal, preferably palladium component. There can be up to 80,
preferably up to 50, more preferably from 1 to 40 and yet more
preferably 5 to 35 weight % of a manganese component based on the
weight of palladium and manganese metal in the pollutant treating
composition. Stated another way, there is preferably about 2 to 30
and preferably 2 to 10 weight % of a manganese component. The
catalyst loading is from 20 to 250 grams and preferably about 50 to
250 grams of palladium per cubic foot (g/ft.sup.3) of catalyst
volume. The catalyst volume is the total volume of the finished
catalyst composition and therefore includes the total volume of air
conditioner condenser or radiator including void spaces provided by
the gas flow passages. Generally, the higher loading of palladium
results in a greater ozone conversion, i.e., a greater percentage
of ozone decomposition in the treated air stream.
[0041] Another illustrative example from U.S. Pat. No. 6,616,903,
comprises a catalyst compositions to treat ozone comprising a
manganese dioxide component and precious metal components such as
platinum group metal components. While both components are
catalytically active, the manganese dioxide can also support the
precious metal component. The platinum group metal component
preferably is a palladium and/or platinum component. The amount of
platinum group metal compound preferably ranges from about 0.1 to
about 10 weight % (based on the weight of the platinum group metal)
of the composition. Preferably, where platinum is present it is in
amounts of from 0.1 to 5 weight %, with useful and preferred
amounts on pollutant treating catalyst volume, based on the volume
of the supporting article, ranging from about 0.5 to about 70
g/ft.sup.3. The amount of palladium component preferably ranges
from about 2 to about 10 weight % of the composition, with useful
and preferred amounts on pollutant treating catalyst volume ranging
from about 10 to about 250 g/ft.sup.3.
[0042] Ozone abatement catalysts, especially those containing a
palladium catalytic component, are effective at temperatures as low
as about 100.degree. F. (37.7.degree. C.), although the rate of
ozone abatement is increased if the air or other gas stream being
treated is heated to a higher temperature. Nonetheless, in some
applications it is highly desirable to have the catalyst
composition be effective over a broad range of inlet gas
temperatures, on the order of about 100.degree. to 300.degree. F.
(21.1.degree. to 148.9.degree. C.). For effective low temperature
operation it is desirable that a high density of the noble
catalytic metal, such as palladium, be attained in highly dispersed
form on the refractory metal oxide support. It has been found that
the desired high density of palladium catalytic component is
enhanced if the soluble palladium salt used to impregnate the
overlayer refractory metal oxide particles is a solution of a
palladium amine salt, such as palladium tetraamine hydroxide or
palladium tetraamine acetate, or palladium nitrate. The use of such
salts, especially in combination with a high porosity refractory
metal oxide support as described below is found to give higher
densities of palladium with improved dispersion on the overlayer
refractory metal oxide than that attainable under similar
conditions with other palladium salts, such as palladium acetate or
palladium chloride. Of course, as noted above, palladium chloride
is preferably not used in any case in order to render the catalyst
composition a non-chloride composition and thereby ameliorate or
prevent corrosion of metal substrates on which the catalyst
composition is carried.
[0043] The downstream volatile organic compound (VOC) abatement
catalysts useful for the practice of the present invention can be
any VOC abatement catalyst system known in the art. For example,
the VOC abatement systems of U.S. Pat. Nos. 3,972,979; 4,053,557,
4,059,675; 4,059,676; 4,059,683; 5,283,041, 5,643,545; 5,578,283;
5,653,949; and 6,319,484, which are hereby incorporated by
reference, are useful for the practice of the present invention.
The abatement composition adsorbs and/or oxidizes volatile organic
compounds, such as hydrocarbons, aldehydes, ketones, etc., in
alternating adsorption and oxidation temperature ranges which lie
within a low to moderate operating temperature range.
[0044] In an illustrative example is U.S. Pat. No. 6,616,903, which
discloses a catalyst composition to treat volatile organic
compounds (VOCs), can comprise from 0.01 weight % to 20 weight %
and preferably 0.5 weight % to 15 weight % of the precious metal
component on a suitable support such as a refractory oxide support,
with the amount of precious metal being based on the weight of the
precious metal, (not the metal component) and the support. Platinum
is the most preferred and is preferably used in amounts of from
0.01 weight % to 10 weight % and more preferably 0.1 weight % to 5
weight % and most preferably 1.0 weight % to 5 weight %. When
loaded onto a monolithic structure the catalyst loading is
preferably about 1 to 150, and more preferably 10 to 100 grams of
platinum per cubic foot (g/ft.sup.3) of catalyst volume. The
preferred refractory oxide support is a metal oxide refractory
which is preferably selected from ceria, silica, zirconia, alumina,
titania and mixtures thereof with alumina and titania being most
preferred.
[0045] Another illustrative example is U.S. Pat. No. 5,653,949,
which discloses a catalyst comprising one or more platinum group
metals, zirconium oxide and at least one of manganese oxide, cerium
oxide or cobalt oxide. Typically, the catalysts contain from about
40 up to about 88 weight % zirconium oxide (as ZrO.sub.2),
preferably from about 60 up to about 85 weight %; and from about 3
up to about 48 weight % of one or more oxides of manganese, cerium
or cobalt, preferably about 10 up to about 30 weight percent. The
platinum group metals may be platinum, palladium and rhodium and
the platinum group metal may be present in the catalyst in an
amount of from about 0.01 to about 8 weight % of the catalyst, and
particularly in an amount of at least about 0.1 weight %.
[0046] In one embodiment the downstream ozone and/or VOC abatement
catalyst is a catalyst composition comprising a catalytic material
coated on a substrate, in which the catalytic material comprises an
undercoat layer or a fine particulate refractory metal oxide and an
overlayer or a refractory metal oxide support on which is dispersed
at least one catalytic metal component.
[0047] Generally, any suitable substrate material may be employed,
including cordierite or other ceramic-like materials, as well as
suitable metals. Typically, the metal substrates have substantially
thinner walls than cordierite or other ceramic-like substrates and
yet provide adequate mechanical strength and better resistance to
thermal shock than do cordierite or similar substrates, and to that
extent are preferred. The thinner walls of metal substrates as
compared to cordierite substrates assist in reducing the pressure
drop sustained by a gas forced through the substrate.
[0048] For abatement catalysts intended for use in aircraft, it is
particularly important that the catalyst be as low weight as
possible. It has been found that a highly satisfactory catalyst of
lightweight can be made in accordance with the teachings of the
present invention by utilizing a metal substrate in which the metal
is aluminum or an aluminum alloy such as an aluminum-magnesium
alloy. Alternatively, the metal substrate may be made of titanium
or a titanium alloy. However, aluminum is lighter than titanium,
less expensive and easier to weld or braze in order to form a
satisfactory metal substrate. Accordingly, metal substrates made of
aluminum or aluminum alloys are, to that degree, preferred. In
particular, an aluminum-magnesium alloy provides greater hardness,
strength and corrosion resistance than aluminum, but cannot readily
be brazed due to the magnesium content. Accordingly,
aluminum-magnesium alloy metal substrates would have to rely on
pins or other mechanical fasteners to provide a rigid metal
substrate structure.
[0049] In one embodiment, the catalysts may comprise a
dual-function catalyst for both the reduction of ozone and the
removal and/or oxidation of volatile organic compounds (VOCs). In
yet another embodiment, the dual-function catalyst comprises
separate catalytic chambers, one consisting of a catalyst for the
reduction of ozone and the second for the removal and/or oxidation
of volatile organic compounds (VOCs).
[0050] The metallic foam trap of the present invention forms an
open or reticulated substrate structure comprising metallic cells
or pores consisting of struts for the cellular walls, see FIG. 2b.
The metallic foam substrate can be further described as a porous
matrix having a plurality of irregularly shaped passages wherein
exhaust gases undergo multiple random twists and turns in traveling
from the upstream side to the downstream side of the trap, see FIG.
2a. This turbulent or tortuous flow path is defined by numerous
apertures, pores, channels or similar structural features that
cause liquid and/or gas to flow therethrough in turbulent or
substantially non-laminar fashion and give the substrate a high
surface area per overall volume of the flow path of the fluid
through the substrate, e.g., features that create a high mass
transfer zone for the fluid therein. In contrast, a dense
substrate, such as a plate, tube, foil and the like, has a
relatively small surface area per overall volume of the flow path
through the substrate regardless of whether it is perforated or
not, and do not substantially disrupt laminar flow therethrough.
The open or reticulated substrate structure of the metallic foam,
importantly not only provides a high mass transfer zone, but such
open structure keeps backpressure low.
[0051] The metallic foam trap of the present invention may be more
readily appreciated by reference again to FIG. 2a, which depicts a
schematic perspective view of a metallic foam trap, and FIG. 2b,
which depicts an enlarged schematic fragmental view of the
three-dimensional network of the metallic foam trap, both intended
as non-limiting embodiments of the invention. Referring to FIGS. 2a
and b, a metallic foam trap 16 is housed within a housing unit 18.
The schematic shows an open network of metallic struts 20 and pores
22, which makes up a torturous pathway for an air inlet stream. The
metallic foam preferentially collects poisonous species primarily
in the gaseous phase and serves as a physical barrier to prevent
poisonous species from contacting the downstream converter
catalysts.
[0052] Since these metallic foam structures have higher surface
areas than dense substrates and since they permit fluid flow
therethrough, they are well-suited for use in preparing trap
members for the trapping of liquid- or gas-borne materials.
Furthermore, the high surface area provides for improved mass
transfer of active species thereby improving the efficiency of the
metallic foam trap.
[0053] Methods for making foamed metal are known in the art, see
e.g., U.S. Pat. No. 3,111,396, which is incorporated herein by
reference, and the use of foamed metal as a carrier for a catalytic
material has been suggested in the art, see e.g., SAE Technical
Paper 971032, entitled "A New Catalyst Support Structure For
Automotive Catalytic Converters" by Arun D. Jatkar, which was
presented at the International Congress and Exposition, Detroit,
Michigan, Feb. 24-27, 1997, and Pestryakov et al., Journal of
Advanced Materials, 1(5), 471-476 (1994). Metallic foams can be
characterized in various ways, some of which relate to the
properties of the initial organic matrix about which the metal is
disposed. Some characteristics of foamed metal substrates
recognized in the art include cell size, density, free volume, and
specific surface area. For example, the surface area may be 1500
times that of a solid substrate having the same dimensions as the
foamed substrate. As mentioned by Pestryakov et al, foamed metal
substrates useful as carriers for catalyst members may have mean
cell diameters in the range of 0.5 to 5 mm, and they may have a
free volume of from about 80 to 98%, e.g., 3 to 15 percent of the
volume occupied by the foamed substrate may constitute metal. The
porosity of the substrate may range from 3 to 80 pores per inch
(ppi), e.g., from 3 to 30 ppi, or from 3 to 10 ppi, or from 3 to 5
ppi. In an illustrative range of 10 to 80 ppi, other
characteristics such as cells per square inch may range from 100 to
6400 and the approximate web diameter may vary from 0.01 inch to
0.004 inch. Such foams may have open-cell reticulated structures,
based on a reticulated/interconnected web precursor. They typically
have surface areas that increase with porosity in the range of from
about 700 square meters per cubic foot of foam (m.sup.2/ft.sup.3)
at about 10 ppi to 4000 m.sup.2/ft.sup.3 at about 60 ppi, etc.
Other suitable metallic foamed substrates have surface areas
ranging from about 200 square feet per cubic foot of foamed metal
(ft.sup.2/ft.sup.3) at about 10 ppi to about 1900 ft.sup.2/ft.sup.3
at about 80 ppi. One such substrate has a specific weight of 500
g/m at a thickness of about 1.6+/-0.2 millimeters with a porosity
of 110 ppi. They may have volume densities in the range of 0.1 to 1
grams per cubic centimeter (g/cc), 0.1 to 0.3 g/cc is also
exemplified.
[0054] Metallic foamed substrates can be formed from a variety of
metals, including iron, titanium, tantalum, tungsten noble metals,
common sinterable metals such as copper, nickel, bronze, etc.,
aluminum, zirconium, etc., and combinations and alloys thereof such
as titanium aluminum alloys, steel, stainless steel, Hastalloy,
Ni/Cr, Inconel (nickel/chromium/iron), Monel (nickel/copper), and
Fecralloy (iron/chromium/aluminum/yttrium). In one embodiment, the
metallic foam substrate is selected from the group consisting of
stainless steel, copper, titanium, Fecralloy, aluminum zirconate,
aluminum titanate, aluminum phosphate, cordierite, mullite and
corundum. For use in aircraft, it is particularly important that
the metallic foam be as low weight as possible, thus, metallic foam
substrates comprising aluminum, copper, titanium, or alloys
thereof, e.g., titanium aluminum alloys, are exemplified. Copper
may be useful because copper is considered to be very reactive with
ozone. For example, the copper metallic foam support can be
pretreated to create an in situ high surface area copper oxide on
the surface of the substrate, which may be useful for the treatment
or removal of ozone from an air intake stream. A suitable metallic
foam substrate for use with the present invention has a volume
occupied by the foamed substrate of about 3 percent to about 10
percent. From about 6 to about 8 percent is also exemplified.
[0055] The metallic foam substrate is preferably coated with a
high-surface area component, said component comprising a
pre-treatment metallic thermal arc sprayed layer and optionally a
washcoat layer, such as aluminum oxide, cerium oxide, zirconium
oxide and copper oxide. The metallic thermal arc sprayed layer
coating can be useful to facilitate the adhesion of the washcoat
layer. The metallic thermal arc sprayed layer of the present
invention can be applied with a thermal spraying process in
general, including plasma spraying, single wire plasma spraying,
high velocity oxy-fuel spraying, combustion wire and/or powder
spraying, electric arc spraying, etc.
[0056] In one aspect of the present invention, electric arc
spraying, e.g., twin wire arc spraying, of a metal (which term, as
used herein and in the claims, includes mixtures of metals,
including without limitation, metal alloys, pseudoalloys, and other
intermetallic combinations) onto metallic foam substrate yields a
structure having unexpectedly superior utility as a substrate for a
washcoat layer, e.g., a refractory metal oxide. Twin wire arc
spraying (encompassed herein by the term "wire arc spraying" and by
the broader term "electric arc spraying") is a known process, see
e.g., U.S. Pat. No. 4,027,367, which is incorporated herein by
reference. Briefly described, in the twin wire arc spray process,
two feedstock wires act as two consumable electrodes. These wires
are insulated from each other as they are fed to the spray nozzle
of a spray gun in a fashion similar to wire flame guns. The wires
meet in the center of a gas stream generated in the nozzle. An
electric arc is initiated between the wires, and the current
flowing through the wires causes their tips to melt. A compressed
atomizing gas, usually air, is directed through the nozzle and
across the arc zone, shearing off the molten droplets to form a
spray that is propelled onto the substrate. Only metal wire
feedstock can be used in an arc spray system because the feedstock
must be conductive. The high particle temperatures created by the
spray gun produce minute weld zones at the impact point on a
metallic substrate. As a result, such electric arc spray coatings
(sometimes referred to herein as "anchor layers") have good
cohesive strength and a very good adhesive bond to the
substrate.
[0057] Thermal arc sprayed layers of a variety of compositions can
be deposited on a metallic foam substrate in accordance with the
present invention by utilizing, without limitation, feedstocks of
the following metals and metal mixtures: Ni, Ni/Al, Ni/Cr,
Ni/Cr/Al/Y, Co/Cr, Co/Cr/Al/Y, Co/Ni/Cr/Al/Y, Fe/Al, Fe/Cr,
Fe/Cr/Al, Fe/Cr/Al/Y, Fe/Ni/Al, Fe/Ni/Cr, 300 and 400 series
stainless steels, and, optionally, mixtures of one or more thereof.
Again, it is particularly important for aircraft applications that
the metallic foam trap of the invention be light weight. In one
embodiment, the metallic thermal arc sprayed layer may comprise
nickel and aluminum. The aluminum may comprise from about 3 to 10
percent, optionally from about 6 to 8 percent, of the combined
weight of nickel and aluminum in the metallic thermal arc sprayed
layer.
[0058] In one embodiment of the present invention, a high surface
area temperature resistant refractory layer can be coated onto a
metallic thermal arc sprayed layer. Useful high surface area
refractory layers include one or more refractory oxides. These
oxides include, for example, silica and metal oxides such as
alumina, including mixed oxide forms such as silica-alumina,
aluminosilicates which may be amorphous or crystalline,
alumina-zirconia, alumina-chromia, alumina-ceria and the like. In
another embodiment, the support may be substantially comprised of
alumina which preferably includes the members of the gamma or
activated alumina family, such as gamma and eta aluminas, and, if
present, a minor amount of other refractory oxide, e.g., about up
to 20 weight percent. Desirably, the active alumina has a specific
surface area of 30 to 300 m.sup.2/g.
[0059] Other suitable materials for the refractory metal oxide
layer include copper, alumina, silica, titania, titania-alumina,
silica-alumina, alumino-silicates, zirconia, titania-zirconia,
aluminum-zirconium oxide, aluminum-chromium oxide, baria-alumina,
etc. Such materials are preferably used in their high surface area
forms. For example, gamma-alumina is preferred over alpha-alumina.
Alternatively, the refractory layer may be made of any suitable
refractory materials such as cordierite, cordierite-alpha-alumina,
silicon nitride, zirconium mullite, spodumene, alumina-silica
magnesia, zirconium silicate, sillimanite, magnesium silicates,
zirconium oxide, petallite, alpha-alumina and alumino-silicates. In
one embodiment of the present invention the refractory layer may be
selected from the group consisting of refractory oxides such as
alumina, titania, zirconia, zirconia-alumina, zirconia-titania,
titania-alumina, lanthana-alumina, baria-zirconia-alumina,
niobia-alumina, and silica-leached cordierite.
[0060] The refractory metal oxide layer is preferably porous in
nature and has a high surface area such as alumina, preferably
gamma-alumina. The choice of the support material is not critical
to the invention. Desirably, the refractory metal oxide support
will have a surface area of between about 5 and about 350
m.sup.2/g. Typically, the support will be present in the amount of
about 1.5 to about 5.0 g/in.sup.3, preferably 2 to 4
g/in.sup.3.
[0061] In yet another embodiment, the metallic foam trap of the
invention contains at least one perforated skewed channel
therethrough to relieve backpressure. The perforated skewed
channel(s) can be literally drilled directly through the metallic
foam at an angle thereby allowing the air inlet stream to mix
between the outer and inner confines passing through the pipe,
without compromising the efficiency of the metallic foam trap. This
open structure through the metallic foam relieves air inlet stream
backpressure.
[0062] The metallic foam trap of this embodiment of the present
invention may be more readily appreciated by reference to FIG. 3,
which depicts a schematic perspective view of a metallic foam trap.
Referring to FIG. 3, the metallic foam trap 24 is housed within a
housing unit 26 and contains a plurality of perforated skewed
channels 28 running therethrough. The perforated skewed channels 28
run at an angle relative to the longitudinal axis of trap 24
thereby allowing the air inlet stream to mix between the outer and
inner confines passing through the pipe, without compromising the
efficiency of the metallic foam trap. Channels 28 do not alter in
any significant manner the tortuous pathway created by the metallic
foam. The perforated skewed channels 28 relieve backpressure. As
seen in FIG. 3, the metallic foam comprises an open network of
pores 30 which along with the metallic struts (not shown), which
form a torturous pathway for an air inlet stream as described
above. The struts can be coated with a metallic thermal arc sprayed
layer and optionally a high surface area temperature resistant
metal oxide, which preferentially collects poisonous species
primarily in the gaseous phase and serves as a physical barrier to
the catalysts of a separate downstream converter for the abatement
of VOCs and/or ozone.
[0063] Although catalysts are generally ill-suited for use with
gases containing inorganic compounds and/or unused hydrocarbons (as
described above), a catalyst may optionally be employed on the
metallic foam. The catalyst may be any known catalyst for the
reduction of volatile organic compounds (VOCs) and/or ozone from an
air stream, as discussed hereinabove. In one embodiment, the
catalyst may be employed in the downstream half of the metallic
foam trap to prevent substantial poisoning thereof.
* * * * *